This invention relates to a hand-held chiselling power tool as is known from U.S. Pat. No. 5,111,890, for example. A pneumatic percussion mechanism has an exciter piston, which is driven in permanent reciprocal movement along an axis. An air spring couples a striker configured as a piston to the exciter piston movement. The percussion mechanism is designed to switch off if the striker travels into a stop instead of striking an intermediate striker. Venting ports are provided for this, which are released by the striker when it is adjacent to the stop. The air spring is vented via the venting ports and thereby deactivated. As soon as the striker is again pushed across the venting ports, the percussion mechanism starts to strike again. Simply by recoiling from the stop, the striker can slide back across the venting ports sufficiently to close them. In this case, there is disadvantageously no automatic deactivation of the percussion mechanism.
The hand-held power tool according to the invention has a tool receptacle for mounting a chiseling tool. A pneumatic percussion mechanism in the hand-held power tool has a striker, an exciter and a guide tube. The striker is configured on the tool for applying impacts in the impact direction. The exciter is motor-driven. The striker is coupled by means of an air spring to the reciprocal movement of the exciter. The striker adjacent to the guide tube is guided along a working axis. The striker is guided during a movement between an impact position and the exciter with a constant guide length on the guide tube, and the guide length is reduced if the impact position is overrun in the impact direction. The hand-held power tool is provided with an inclined guide which inclines the striker relative to the working axis if the impact position is overrun.
During operation, the striker flies in the impact direction to the impact position and there strikes the tool or an intermediate striker (riveting die). If the user is not working with the hand-held power tool, i.e. the tool is not pressing on a substrate, the striker can slide beyond the impact position.
The axial guiding of the striker is deliberately reduced to activate the striker into an inclined position relative to the working axis. The inclined position can encourage the striker to come to rest in order to promote the switching off of the percussion mechanism. The striker travels into the inclined guide only after overrunning the impact position. The striker reaches the inclined guide not later than after an axial impact. The striker, which is normally guided carefully in a coaxial direction relative to the working axis during operation, is deliberately inclined. The inclining hinders the movement of the striker and promotes a resting position for switching off the percussion mechanism, e.g. behind the venting ports.
An embodiment envisages that venting ports are provided for venting the air spring. The venting ports are arranged in such a way that the striker shuts off the air spring opposite the venting ports when the striker is in the impact direction before the impact position, and otherwise releases the venting ports. The air springs can thus be preferably vented as soon as the striker slides beyond the impact position.
The inclined guide can have a radial bearing surface facing the working axis and the striker can have a radial sliding surface in contact with the bearing surface. One, preferably exactly one, of the bearing surface or sliding surface is configured asymmetrically to the working axis. The inclined guide effectuates a resulting force in an angular direction on the striker, the force not being balanced due to the lack of revolving symmetry. Consequently, the striker inclines. The striker is thereby advantageously guided in the guide tube with its rear end in the impact direction.
The bearing surface or the sliding surface can have a projection protruding in a radial direction in only one angular direction. An axis of the bearing surface or an axis of the gliding surface can be offset parallel to the working axis or inclined relative to the working axis.
The striker can have a piston and a push rod. The piston seals the pneumatic chamber in the guide tube and is positively driven by the guide tube. The push rod is downstream of the piston in the impact direction and forms the impact surface, which impacts on the intermediate striker or the tool. The push rod can have a smaller diameter than the piston and is preferably not guided by the guide tube. The inclined guide guides the push rod provided the striker is advanced across the impact position.
The division of striker into piston and push rod can only be understood in terms of its function and geometry. Piston and striker are a monolithic body; piston and striker cannot be separated from each other or pushed towards each other.
The push rod can have a radial surface configured asymmetrically to the axis of the piston. A midpoint in the contour of the radial surface does not lie on the axis.
Further features and advantages of the invention will emerge from the following description of exemplary embodiments shown in the accompanying drawings.